1. Field of the Invention
The present invention relates to a method of producing a composite material, a method of producing a piezoelectric actuator, a method of producing an ink-jet head, and a piezoelectric actuator.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2001-54946 discloses an example of a piezoelectric actuator used, for example, in an ink-jet head or the like. The ink-jet head includes a channel forming body, which has pressure chambers and nozzles. Each of the pressure chambers communicates with an opening of one of the nozzles. The piezoelectric actuator includes a substrate (a vibration plate), which is arranged on the channel forming body so as to close the opening of each of the pressure chambers. Lower electrodes, piezoelectric layers, and upper electrodes are stacked or laminated on the substrate. When an electric field is applied between each of the lower electrodes and the associated upper electrodes, the piezoelectric layer deforms, thereby warping the substrate. This exerts pressure to the ink in the associated pressure chamber so as to discharge the ink through the associated nozzle.
As a method of producing such a piezoelectric actuator, there is a method called the aerosol deposition (AD) method disclosed in Japanese Patent Application Laid-open No. 2001-54946. In this method, a substance (aerosol) in which fine particles, of a piezoelectric material such as Lead Zirconate Titanate (PZT) or the like, is dispersed in a gas, is jetted toward a surface of a substrate such that the fine particles are collided and deposited onto the substrate, thereby forming a piezoelectric film.
The piezoelectric film formed by the AD method needs to be subjected to an annealing treatment so as to impart, to the piezoelectric film, piezoelectric characteristics necessary for warping the substrate sufficiently.
However, when an annealing treatment was performed at a high temperature, for example exceeding 600° C., an element contained in the substrate diffuses into the piezoelectric film and degrade the piezoelectric characteristic of the film in some cases. In particular, in recent years, it has been demanded that stainless steel which is cheap and highly workable be used as a substrate. However, with the stainless steel, this problem of diffusion becomes prominent since stainless steel contains metallic elements such as Fe, Cr and the like which are easily diffuse into a piezoelectric film. Therefore, in order to improve the piezoelectric characteristic of a piezoelectric film, a layer of insulative oxide such as alumina or the like is provided as a diffusion-preventive layer between the piezoelectric film and the substrate. In such a case, a lower electrode is provided between the diffusion-preventive layer and the piezoelectric layer so that electric field can be applied to the piezoelectric layer.
However, in a case of stacking a large number of layers and when the piezoelectric layer is annealed at a high temperature, stress is developed at interfaces of stacked layers due to the differences in coefficients of thermal expansion between the materials with which the layers are respectively formed. Due to the stress, exfoliation of the laminated layers is easily caused.
In producing an ink-jet head, it is preferable that an ink channel forming body is formed of metallic material such that minute or fine ink channels can be formed in the ink channel forming body easily. Also, with respect to a substrate for a piezoelectric actuator to be joined to the channel forming body by thermo-compression bonding, it is preferable that the substrate is formed of a metal having a coefficient of thermal expansion similar to that of the metal material forming the channel forming body, namely the substrate is formed of a same metallic material to that forming the channel forming body, in order to avoid a problem or inconvenience such as warpage of the substrate which can occur when the substrate is joined to the channel forming body by thermo-compression bonding. However, when the substrate is metallic, a metallic element contained in the substrate is likely to diffuse into the piezoelectric layer. Accordingly, although it is necessary to provide a diffusion-preventive layer between the substrate and the piezoelectric layer, it is not always easy to ensure the adherence by a conventional method between a large numbers of stacked layers as described above.